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TONE, use references, -OR (Tyche has nothing to do with Sedna)
Undid revision 456840974 by Kheider (talk) Tyche theory throws more doubt on Nemesis, so it is a part of the story. This is no different than the "Ancient star" theory-- neither are proven.
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===Ancient Non-Companion Star Passings===
===Ancient Non-Companion Star Passings===


Brown has stated that it is more likely that one or more non-companion stars, passing near the Sun billions of years ago, could have pulled Sedna out into its current orbit.<ref name="discover2006"/> In 2004, Kenyon forwarded this explanation after analysis of Sedna's orbital data and computer modeling of possible ancient non-companion star passes.<ref name=Kenyon/>
Recently, Brown has stated that it is more likely that one or more non-companion stars, passing near the Sun billions of years ago, could have pulled Sedna out into its current orbit{{citation needed|October 2011}}. Kenyon has also forwarded this explanation after analysis of Sedna's orbital data and computer modeling of possible ancient non-companion star passes.<ref name=Kenyon/>


===Tyche Theory===
===Tyche Theory===


Other scientists have postulated that rather than being a Nemesis-like object, that an as-yet undiscovered very large planet in the size range of four Jupiter masses is a more likely cause of perturbations to the Oort cloud. This theorized very large planet has been nicknamed [[Tyche]].
Other scientists have postulated, after study of Sedna's orbit, and also other outer solar system object orbital data, that rather than being a Nemesis-like object, that an as-yet undiscovered very large planet in the size range of four Jupiter masses, orbiting much closer to Sedna than the theorized Nemesis, is a more likely cause of it's orbital perturbation.{{Citation needed|date=October 2011}} This theorized very large planet has been nicknamed [[Tyche]].{{Citation needed|date=October 2011}}


==Past, current and pending searches for Nemesis==
==Past, current and pending searches for Nemesis==

Revision as of 15:48, 22 October 2011

Template:Distinguish2

Artist's conception of Nemesis as a red dwarf seen from a nearby debris field with the Sun visible in the center.

Nemesis is a hypothetical hard-to-detect red dwarf star,[1] white dwarf star[2] or brown dwarf,[3] originally postulated in 1984 to be orbiting the Sun at a distance of about 50,000 to 100,000 AU (about 0.8-1.5 light-years), somewhat beyond the Oort cloud,[3] to explain a perceived cycle of mass extinctions in the geological record, which seem to occur once per 26 million years.[3]

Counter-theories also exist that other forces, like close ancient passings of other stars, or the angular effect of the galactic gravity plane working against the outer solar orbital plane, may be the cause of orbital perturbations of some outer solar system objects.[4] In 2010, two astronomers, Melott and Bambach analysed earlier data on outer solar system object orbital patterns and announced that their findings suggest Nemesis couldn't possibly exist.[2] In 2011, Coryn Bailer-Jones did an analysis of craters on the Earths surface and reached the conclusion that the earlier findings of simple periodic patterns (implying periodic comet showers dislodged by a hypothetical Nemesis star) to be statistical artifacts, and found that the crater record shows no evidence for Nemesis.[5] The Infrared Astronomical Satellite (IRAS) failed to discover Nemesis in the 1980s. The 2MASS astronomical survey, which ran from 1997 to 2001, failed to detect a star, or brown dwarf, in the solar system.[3]

Using newer and more powerful infrared telescope technology, able to detect brown dwarfs as cool as 150 Kelvin out to a distance of 10 light-years from the sun,[6] preliminary results from the Wide-field Infrared Survey Explorer (WISE survey) have not, to date, detected Nemesis, although the analysis of the full survey is not yet complete.[7] Scientists no longer think an object like Nemesis could exist because if it did it would have been detected long ago in infrared sky surveys.[8]

Claimed periodicity of mass extinctions

In 1984, paleontologists David Raup and Jack Sepkoski published a paper claiming that they had identified a statistical periodicity in extinction rates over the last 250 million years using various forms of time series analysis.[9] They focused on the extinction intensity of fossil families of marine vertebrates, invertebrates, and protozoans, identifying 12 extinction events over the time period in question. The average time interval between extinction events was determined as 26 million years. At the time, two of the identified extinction events (Cretaceous-Tertiary and Late Eocene) could be shown to coincide with large impact events. Although Raup and Sepkoski could not identify the cause of their supposed periodicity, they suggested a possible non-terrestrial connection. The challenge to propose a mechanism was quickly addressed by several teams of astronomers.

Development of the Nemesis hypotheses

Two teams of astronomers, Whitmire and Jackson, and Davis, Hut, and Muller, independently published similar hypotheses to explain Raup and Sepkoski's extinction periodicity in the same issue of the journal Nature.[10][11] This hypothesis proposes that the Sun may have an undetected companion star in a highly elliptical orbit that periodically disturbs comets in the Oort cloud, causing a large increase of the number of comets visiting the inner Solar System with a consequential increase of impact events on Earth. This became known as the "Nemesis" or "Death Star" hypothesis.

If it does exist, the exact nature of Nemesis is uncertain. Richard A. Muller suggests that the most likely object is a red dwarf with magnitude between 7 and 12,[12] while Daniel P. Whitmire and Albert A. Jackson argue for a brown dwarf.[10] If a red dwarf, it would exist in star catalogs, but its true nature would only be detectable by measuring its parallax; due to orbiting the Sun it would have a very low proper motion and would escape detection by proper motion surveys that have found stars like the 9th-magnitude Barnard's star.

Muller, referring to the date of a recent extinction at 5 million years before the present day, posits that Nemesis is 1.0 to-[convert: unknown unit] distant at present and suggests it is located (supported by Yarris, 1987) near Hydra, based on a hypothetical orbit derived from original apogees of a number of atypical long-period comets that describe an orbital arc meeting the specifications of Muller's hypothesis.

Other possible evidence: questions about orbital path of Sedna

Sednas Perturbed Orbit

The planetoid Sedna has an extra-long and unusual elliptical orbit around the Sun,[13]ranging between 76 and 975 AU. Sedna’s orbit is estimated to last between 10.5 and 12 thousand years. Its discoverer, Michael Brown of Caltech, noted in a Discover magazine article that Sedna’s location seemed to defy reasoning:[14] "Sedna shouldn't be there," said Brown. "There's no way to put Sedna where it is. It never comes close enough to be affected by the Sun, but it never goes far enough away from the Sun to be affected by other stars."[14] Brown therefore originally postulated that a massive unseen object may be responsible for Sedna’s anomalous orbit.[13]

Ancient Non-Companion Star Passings

Recently, Brown has stated that it is more likely that one or more non-companion stars, passing near the Sun billions of years ago, could have pulled Sedna out into its current orbit[citation needed]. Kenyon has also forwarded this explanation after analysis of Sedna's orbital data and computer modeling of possible ancient non-companion star passes.[4]

Tyche Theory

Other scientists have postulated, after study of Sedna's orbit, and also other outer solar system object orbital data, that rather than being a Nemesis-like object, that an as-yet undiscovered very large planet in the size range of four Jupiter masses, orbiting much closer to Sedna than the theorized Nemesis, is a more likely cause of it's orbital perturbation.[citation needed] This theorized very large planet has been nicknamed Tyche.[citation needed]

Past, current and pending searches for Nemesis

The Infrared Astronomical Satellite (IRAS) failed to discover Nemesis in the 1980s. The 2MASS astronomical survey, which ran from 1997 to 2001, failed to detect a star, or brown dwarf, in the solar system.[3] If Nemesis exists, it may be detected by Pan-STARRS or the planned LSST astronomical surveys.

In particular, if Nemesis is a red dwarf star or a brown dwarf, the WISE mission (an infrared sky survey that covered most of our solar neighborhood in movement-verifying parallax measurements) is expected able to find it.[13] WISE can detect 150 Kelvin brown dwarfs out to 10 light-years.[6] But the closer a brown dwarf is the easier it is to detect.[6] Preliminary results of the WISE survey were released on 14 April 2011.[15] The final release of analyzed results is to be released in March 2012.[16]

Cultural references

  • Nemesis, a book about a civilization affected by an unknown additional star, by Isaac Asimov.

See also

References

  1. ^ Leader-Post, "Scientists claim killer star exists", 22 Feb 1984, Page B6, Associated Press
  2. ^ a b Space.com, "Sun's Rumored Hidden Companion May Not Exist After All", 20 July 2010, Clara Moskowitz
  3. ^ a b c d e Leslie Mullen (Astrobiology Magazine) (11 March 2010). "Sun's Nemesis Pelted Earth with Comets, Study Suggests". Space.com. Retrieved 2010-08-22.
  4. ^ a b Kenyon, Scott J. (2004). "Stellar encounters as the origin of distant Solar System objects in highly eccentric orbits". Nature. 432 (7017): 598–602. arXiv:astro-ph/0412030. Bibcode:2004Natur.432..598K. doi:10.1038/nature03136. PMID 15577903. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  5. ^ "Nemesis is a myth". Max Planck. August 1, 2011. Retrieved 2011-10-07.
  6. ^ a b c "Science: Brown Dwarfs". WISE/NASA. Retrieved 2007-12-28.
  7. ^ Kirkpatrick, J. Davy (2011). "The First Hundred Brown Dwarfs Discovered by the Wide-field Infrared Survey Explorer (WISE)". arXiv:1108.4677 [astro-ph.SR]. {{cite arXiv}}: Unknown parameter |accessdate= ignored (help); Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |version= ignored (help)
  8. ^ David Morrison (August 2, 2011). "Scientists today no longer think an object like Nemesis could exist". NASA Ask An Astrobiologist. Retrieved 2011-10-22.
  9. ^ Raup, D.M. (1 February 1984). "Periodicity of Extinctions in the Geologic Past" (PDF). Proceedings of the National Academy of Sciences. 81 (3): 801–805. Bibcode:1984PNAS...81..801R. doi:10.1073/pnas.81.3.801. PMC 344925. PMID 6583680. Retrieved 30 April 2007. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  10. ^ a b Whitmire, D.P. (1984). "Are periodic mass extinctions driven by a distant solar companion?". Nature. 308 (5961): 713–715. Bibcode:1984Natur.308..713W. doi:10.1038/308713a0. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  11. ^ Davis, M. (1984). "Extinction of species by periodic comet showers". Nature. 308 (5961): 715–717. Bibcode:1984Natur.308..715D. doi:10.1038/308715a0. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  12. ^ http://muller.lbl.gov/pages/lbl-nem.htm Muller.lbl.gov Retrieved on 05-19-07
  13. ^ a b c "Astrobiology Magazine", "Cosmic Evolution" Section, "Getting WISE about Nemesis" 03/11/10, Author: Leslie Mullen http://www.astrobio.net/exclusive/3427/getting-wise-about-nemesis
  14. ^ a b Cal Fussman (May 27, 2006). "The Man Who Finds Planets". Discover magazine. Retrieved 2011-10-20.
  15. ^ "NASA - WISE Delivers Millions of Galaxies, Stars, Asteroids". Nasa.gov. Retrieved 2011-06-15.
  16. ^ "Can WISE Find the Hypothetical 'Tyche'?". NASA/JPL. February 18, 2011. Retrieved 2011-06-15.
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